A gas turbine engine, typically used as a source of propulsion in aircraft, operates by drawing in ambient air, combusting that air with a fuel, and then forcing the exhaust from the combustion process out of the engine. In many gas turbine engines a fan rotates to draw air into the engine; however, the fan is not a necessity for all gas turbine engines. A compressor section, having low and high pressure compressors in dual-spool compressor designs, has a plurality of axially aligned stages. Each of these stages includes a rotor, having a plurality of radially outwardly extending and rotating blades, and a stator, having a plurality of radially inwardly extending and stationary vanes. The rotor of each stage compresses air, while the stator realigns the air for optimal compression by the next stage. The compressed air flows from the compressor section through a diffuser, to be slowed, and into the combustor, where it is split. A portion of the air is used to cool the combustor while the rest is mixed with a fuel and ignited.
An igniter generates an electrical spark in the combustor to ignite the air-fuel mixture. The products of the combustion then travel out of the combustor as exhaust and into a turbine section. The turbine section, having low and high pressure turbines in dual-spool turbine designs, also has a plurality of axially aligned stages. Similar to the compressor, each of the turbine stages includes a stator, having a plurality of radially inwardly extending stationary vanes, and a rotor, having a plurality of radially outwardly extending and rotating blades. Each rotor of the turbine is forced to rotate as the exhaust impinges upon the blades, while each stator re-aligns the exhaust for optimal impingement upon the rotor of the next turbine stage. The fan, compressor section, and turbine section are connected by concentrically mounted engine shafts running through the center of the engine. Thus, as the turbine rotors are rotated by the exhaust, the fan and corresponding compressor rotors are also rotated to bring in and compress new air. Once started, it can thereby be seen that this process is self-sustaining.
Seals surround the rotors of the compressors and turbines to reduce the air/exhaust bypassing the blades of these rotors. Air which bypasses the compressor rotors is not properly compressed and therefore hampers combustion, while exhaust which bypasses the turbine rotors reduces engine efficiency as energy is not fully extracted from the bypassing exhaust. Thus, the seals must be as close as possible to the blades of these rotors without touching the blades, as such contact would damage the seals and blades and possibly hamper rotation, while excessive spacing would allow more air/exhaust to bypass the rotor than is desired, thereby hampering combustion and efficiency. However, maintaining this close seal is difficult since the diameters of these rotors change throughout the operation of the engine. Thermal growth due to varying temperatures in the air/exhaust, as well as centrifugal growth due to varying rotational speeds, causes the diameter of the rotors to change during operation.
In an effort to match the growth of the engine rotors during operation, clearance control rings have been developed to maintain the close seals necessary for optimum engine operation. While effective, many rotors have segmented cases surrounding the rotors to facilitate easier assembly of, and maintenance on, the rotors. Current clearance control rings, however, negate many of the benefits of such segmented cases since the current clearance control rings are of full hoop designs, and therefore require stage-by-stage assembly and disassembly. It can thus be seen that a need exists for a clearance control ring which can maintain a close seal with an active rotor, while not negating the advantages of the segmented rotor case.